(1) Field of the Invention
The present invention relates generally to a vehicle orientation detecting device for an automotive vehicle or another vehicle which derives a directional representative signal with respect to the orientation of a geomagnetic field, and more particularly to a vehicle orientation detecting device mounted in the automotive vehicle which provides an accurate directional indication by correcting an error caused by the magnetism of the vehicle itself in the vicinity of the vehicle orientation detection device with a circuitry.
(2) Description of the Prior Art
When a vehicle orientation detecting device is mounted in, e.g. an automotive vehicle, there arises a problem in that the vehicle body has a magnetism with a direction and magnitude particular to the vehicle body; the vehicle body magnetism has an effect on the indication of the vehicle orientation detecting device.
To correct such an erroneous indication of the vehicle orientation caused by the magnetism of the vehicle body, various error correcting means for the vehicle orientation detecting device have been considered.
For example, a permanent magnet has been installed in the vicinity of a geo-magnetisn detecting coil of a vehicle orientation detecting device. The permanent magnet produces a magnetic field having the same magnitude and opposite direction as the magnetism of the vehicle body so that the effect of the vehicle body magnetism acting on the geomagnetism detecting coil is cancelled. However, the positioning of the permanent magnet is time-consuming and complicated since the vehicle must be placed at one of two mutually orthogonal directions, i.e. north-south, and east-west, to adjust the position of the permanent magnet. In addition, once the magnet has been positioned, the position of the permanent magnet can drift due to the temperature changes and fluctuations of the vehicle body, etc.
As another example, the permanent magnet is replaced by an electromagnetic coil having two wires wound around a disc-shaped core so as to intersect at right angles. The vehicle body magnetism is cancelled by adjusting the magnitude and direction of currents flowing through each wire of the electromagnetic coil. Although positioning of the electromagnetic coil itself is not necessary, such electromagnetic coil has the disadvantage of requiring currents as large as 500 to 800 mA, assuming that each wire has about 1000 turns. Supplying such current magnitudes the electromagnetic coil at a power supply voltage of about 100 V, as is necessary for this purpose, heats the electromagnetic coil excessively. Consequently, a cooling means must be installed for the electromagnetic coil, an impractical requirement for the vehicle.
Therefore, as described above, the conventional means for canceling the influence by the vehicle body magnetism are complex in positioning or construction.